| The kinetic mechanisms of Late Mesozoic magmatism in South China have long been the focus of research by scholars at home and abroad.A large number of studies have been carried out on the Late Mesozoic magmatism in South China and numerous kinetic models have been proposed.These kinetic models can be divided into two main categories:those that suggest that the Late Mesozoic magmatism in South China was controlled by the coastal Pacific tectonic domain,and those that suggest that it was related to the Tethys tectonic domain.However,most of these kinetic models are based on the Late Mesozoic coastal magmatic rocks of South China,which cannot explain well the mechanism of Late Mesozoic magmatism in the inland areas of South China.This paper therefore selects the Late Mesozoic rocks in the southeastern Guangxi region of inland South China as the object of study,and carries out systematic petrological,petrographic,zircon U-Pb chronology and Lu-Hf isotope geochemical studies on the Nandu granodiorite,Liuwang quartz porphyry and Jinzhu dacite to further define the geodynamic background of Late Mesozoic magmatism in the southeastern Guizhou region.The Nandu granodiorite intrusion age is 161.8±1.2 Ma,with a high Si O2 content,and shows high potassium-calcium-alkaline,weakly peraluminous characteristics,and is a Type I granite.The sample has a high total rare earth content,with a clear differentiation between light and heavy rare earths（LREE/HREE of 3.16～4.98 and（La/Yb）N of 8.05-15.96）,enrichment in LILE and LREE,deficiency in HFSE,and weak or no negative anomalies in Nb-Ta elements.?Hf（t）values range from-23.26 to-2.48,spanning a wide range.The source area of the Nandu granodiorite is judged to have been formed by remelting of metamorphic heterogeneous sandstones from the lower crust of the Middle-Palaeo-Palaeozoic and mixed with minor mantle material.The intrusive ages of the Liuwang quartz porphyry and the Jinzhu dacite rock are 98±0.64Ma and 98±0.19 Ma respectively,both of which are products of early Late Cretaceous magmatism.The Liuwang quartz porphyry is strongly peraluminous and similar to highly differentiated S-type granites（differentiation index（DI）of 93.82～94.97）.Total rare earths are high,and light and heavy rare earths are not clearly differentiated（LREE/HREE=1.14-2.03,（La/Yb）N=0.47～1.04）.The sample is enriched in LILE,deficient in HFSE,and has obvious negative Eu anomalies,and is analysed by the Hf isotopic signature of zircon to be formed by remelting of crustal material in the Middle Ages.The petrographic characteristics of the Jinzhu dacite indicate that they are acidic igneous rocks with high Ca-Pb metamorphic series.The sample is enriched in LILE and LREE,with a significant loss of Nb-Ta-Ti elements,and is analysed by the Hf isotopic signature of zircon as a result of remelting of ancient crustal material and mingling of partially molten material from the enriched mantle.The above information indicates that the southeastern Guangxi region was influenced by the coastal Pacific tectonic domain from at least the Late Jurassic,and that the magmatic activity in the region was mainly caused by the upwelling of the soft current circle and lithospheric extension and thinning of the ancient Pacific plate plate plate subduction and retreat,which lasted at least until the Early Cretaceous.The formation of the Liuwang quartz porphyry and the sinistral Jinzhu dacite indicates that an active continental margin arc environment existed in the Late Cretaceous inland of southern China,and that this environment was caused by the subduction-tearing of the New Tethys Plate to the continental plate in southern China.The Late Jurassic-Early Cretaceous inland magmatism in southern China was mainly influenced by the Pacific Coastal Tectonic Domain,while the Middle to Late Cretaceous was probably controlled by the combined Pacific Coastal Tectonic Domain and the Tethys Tectonic Domain,with the Tethys Tectonic Domain being the dominant influence. |
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